Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: How precisely can a right angle be measured?
Replies: 7   Last Post: Apr 5, 2013 7:17 PM

 Messages: [ Previous | Next ]
 Bart Goddard Posts: 1,706 Registered: 12/6/04
Re: How precisely can a right angle be measured?
Posted: Apr 4, 2013 7:28 PM

pete <pfiland@mindspring.com> wrote in news:515E07CA.1347
@mindspring.com:

> Tom Potter wrote:
>>
>> "pete" <pfiland@mindspring.com> wrote in message
>> news:515C5712.746@mindspring.com...

>> > Tom Potter wrote:
>> >>
>> >> How would one measure a right angle
>> >> without using geometry,
>> >> or the 3-4-5 relationship,
>> >>
>> >> and how precisely can a right angle be measured?

>> >
>> > I place a straight edge
>> > approximately perpendicular to a straight line,
>> > and then I maneuver the edge to make adjacent angles
>> > of equal size.
>> >
>> > It's very easy to accurately compare adjacent angles.
>> >
>> > I can't state the precission.
>> >
>> > --
>> > pete

>>
>> Okay,
>> let's assume that a laser beam is a "straight line"
>> over the range of interest,
>>
>> and let us "place a straight <laser beam>
>> approximately perpendicular to <the> straight line,"
>>
>> and juggle the "approximately perpendicular straight line"
>> until the "adjacent angles" are equal,
>>
>> how do we compare the "adjacent angles"?

>
> The best that I can explain it
> is just that it is very easy to see, simply by looking,
> which of two adjacent supplementary angles,
> if either, is bigger.
>
> http://regentsprep.org/Regents/math/geometry/GP5/SuppAng.gif
> you should be able to tell that angle 2,
> is bigger than angle 1,
> just by looking at them.
>
> Try it.
> Get some paper, a straight edge, and a pencil.
> Draw a line.
> Reposition the straight,
> and draw a perpendicular line.
>
> You shouldn't need a protractor
> to be able to tell if you got it right.
>

I would set the point of my compass at the point of intersection.
Then draw a circle about that point. The circle intersects the
line at A and B, and the perpendicular at C. Set the point of the
compass at C and the pencil at A and draw another circle. If it
falls short of B or over shoots B, then you'll know which angle is
bigger. Or does that violate the rule of "without using geometry"?

B.

Date Subject Author
4/4/13 Tom Potter
4/4/13 pete
4/4/13 Bart Goddard
4/5/13 Brian Q. Hutchings
4/5/13 pete
4/5/13 Brian Q. Hutchings